Controversial Russian media mogul Mikhail Lesin, who helped found the RT English-language television network, has been found dead at a Washington hotel. He was 57.

RT, formerly known as Russia Today, said the former minister of media affairs died of a heart attack.

“Lesin died. It’s impossible to believe this,” tweeted Margarita Simonyan, editor-in-chief of RT, which is state funded.

ABC News, quoting a Russian and a US official, reported late Friday that Lesin had been found in Washington’s Dupont Circle Hotel the day before.

A controversial figure, Lesin had been accused of limiting press freedom in Russia.

In a terse statement, Russian President Vladimir Putin’s spokesman Dmitry Peskov told reporters late Friday that the “President highly values the enormous contribution Mikhail Lesin made helping establish Russian media”.

The Washington police would not confirm his death, saying only that it was investigating the death of someone on the block where the hotel is located in a fashionable area of Washington.

US officials notified the Russian embassy of Lesin’s death and authorities from both countries are trying to determine the circumstances in which he died.

Lesin was Russia’s minister of press, television and radio between 1999 and 2004 and later served as a Kremlin aide.

In 2013, he became head of Gazprom-Media Holding, the media arm of state energy giant Gazprom.